Control circuit for fan

ABSTRACT

A control circuit includes a temperature measuring module, a fan controller, and a conversion circuit. The temperature measuring module measures temperature of an electronic element. The fan controller stores a data table, the data table includes a number of temperature values and duty cycle of a number of pulse width modulation (PWM) signals corresponding to the temperature values. The fan controller reads the measured temperature from the temperature measuring module and outputs a control signal according to the stored data table. The conversion circuit is connected between the fan controller and a fan connector, to receive the control signal from the fan controller and convert the control signal to a PWM signal, and output the PWM signal to a fan connected to the fan connector, to control a rotation speed of the fan.

BACKGROUND

1. Technical Field

The present disclosure relates to a control circuit for a fan.

2. Description of Related Art

At present, a number of fans are arranged in a computer for dissipating heat from electronic elements of the computer. However, rotation speeds of the fans are not controlled automatically for saving power. Therefore, there is a room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a block diagram of an embodiment of a control circuit for a fan.

FIG. 2 is a circuit diagram of the control circuit of FIG. 1.

DETAILED DESCRIPTION

The disclosure, including the accompanying drawings, is illustrated by way of examples and not by way of limitation. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”

FIG. 1 shows an embodiment of a control circuit 1 for controlling rotation speed of a fan 16. The control circuit 1 includes a temperature measuring module 10, a fan controller 12, and a conversion circuit 126.

The temperature measuring module 10 is arranged adjacent to an electronic element 2, such as a display chip, to measure a temperature of the electronic element 2 and store the measured temperature in a storage unit inside the temperature measuring module 10. In one embodiment, the temperature measuring module 10 is a temperature sensor, which has a system management bus (SMBus) interface.

The fan controller 12 includes a first interface 120 and a second interface 122. The first interface 120 is connected to the temperature measuring module 10. The second interface 122 is connected to the conversion circuit 126. The fan controller 12 stores a data table, which includes a plurality of temperature values and corresponding duty cycles of a plurality of pulse width modulation (PWM) signals. The fan controller 12 reads the measured temperature stored in the temperature measuring module 10 and determines a duty cycle of a PWM signal corresponding to the measured temperature, according to the stored data table. The fan controller 12 outputs a control signal to the conversion circuit 126. The conversion circuit 126 converts the control signal to a corresponding PWM signal and outputs the PWM signal to the fan 16 through the fan connector 18, to control the rotation speed of the fan 16. At the same time, the fan controller 12 receives a feedback as to the rotation speed of the fan 16 through a measuring pin TACH of the fan connector 18 when the fan 16 operates normally.

Referring to FIG. 2, the temperature measuring module 10 includes a temperature sensor chip U1. A serial data pin SDA of the temperature sensor chip U1 is connected to a pin A of the first interface 120 through a resistor R2. A serial clock pin SCL of the temperature sensor chip U1 is connected to a pin B of the first interface 120 through a resistor R1. The serial clock pin SCL and the serial data pin SDA of the temperature sensor chip U1 are connected to a power source P3V3 through resistors R3 and R4 respectively. An alarm pin ALERT of the temperature sensor chip U1 is connected to the power source P3V3 through a resistor R5. A ground pin GND of the temperature sensor chip U1 is grounded. A voltage pin VCC of the temperature sensor chip U1 is connected to the power source P3V3 and is also grounded through a capacitor C1. A data pin AO of the temperature sensor chip U1 is grounded through a resistor R6. Data pins A1 and A2 of the temperature sensor chip U1 are connected to the power source P3V3 through resistors R7 and R8 respectively. In one embodiment, the power source P3V3 outputs 3.3 volts (V).

The conversion circuit 126 includes transistors Q1 and Q2. A pin C of the second interface 122 is connected to the power source P3V3 through a resistor R9 and is also connected to a base of the transistor Q1 through a resistor R10. An emitter of the transistor Q1 is grounded. A collector of the transistor Q1 is connected to the power source P3V3 through a resistor R11 and is also connected to a base of the transistor Q2. An emitter of the transistor Q2 is grounded. A collector of the transistor Q2 is connected to the power source P3V3 through a resistor R12 and is also connected to a control pin PWM of the fan connector 18. A pin D of the second interface 122 is grounded through resistors R13 and R14 in sequence. A capacitor C2 is connected to the resistor R14 in parallel. A node between the resistors R13 and R14 is connected to a power source P12V through resistors R15 and R16 in sequence. A node between the resistors R15 and R16 is connected to an anode of a diode D1. A cathode of the diode D1 is connected to the power source P12V. In one embodiment, the power source P12V outputs 12V.

The anode of the diode D1 is also connected to a measuring pin TACH of the fan connector 18. A power pin VCC of the fan connector 18 is connected to the power source P12V and also grounded through a capacitor C3. A ground pin GND of the fan connector 18 is grounded.

In use, the temperature sensor chip U1 measures a temperature of the electronic element 2 and outputs the measured temperature to the fan controller 12 through the pins A and B of the first interface 120. The fan controller 12 receives the measured temperature and determines duty cycle of a PWM signal corresponding to the measured temperature according to the stored data table, and outputs a control signal to the conversion circuit 126 through the pin C of the second interface 122. The conversion circuit 126 receives the control signal and converts the control signal to a PWM signal, and outputs the PWM signal to the fan 16 through the control pin PWM of the fan connector 18, to control the rotation speed of the fan 16. In one embodiment, when the pin C of the second interface 122 outputs a high level signal, the transistor Q1 is turned on and the transistor Q2 is turned off. The fan 16 receives a high level signal from the conversion circuit 126 through the control pin PWM of the fan connector 18. When the pin C of the second interface 122 outputs a low level signal, the transistor Q1 is turned off and the transistor Q2 is turned on. The fan 16 receives a low level signal from the conversion circuit 126 through the control pin PWM of the fan connector 18.

At the same time, the fan controller 12 receives feedback as to rotation speed of the fan 16 through the pin D of the second interface 122 and the measuring pin TACH of the fan connector 18 when the fan 16 operates normally.

The control circuit 1 measures the temperature of the electronic element 2 through the temperature sensor chip U1, and determines duty cycle of a PWM signal according to the measured temperature to the fan 16, to control the rotation speed of the fan 16.

The foregoing description of the embodiments of the disclosure has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of everything above. The embodiments were chosen and described in order to explain the principles of the disclosure and their practical application so as to enable others of ordinary skill in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those of ordinary skills in the art to which the present disclosure pertains without departing from its spirit and scope. Accordingly, the scope of the present disclosure is defined by the appended claims rather than by the foregoing description and the exemplary embodiments described therein. 

What is claimed is:
 1. A control circuit applicable to control a fan, the control circuit comprising: a temperature measuring module to measure temperature of an electronic element; a fan controller to store a data table, wherein the data table comprises a plurality of temperature values and duty cycle of a plurality of pulse width modulation (PWM) signals corresponding to the plurality of temperature values, the fan controller reads the measured temperature from the temperature measuring module and outputs a control signal according to the stored data table; and a conversion circuit connected between the fan controller and a fan connector, to receive the control signal from the fan controller and convert the control signal to a PWM signal, and output the PWM signal to the fan connected to the fan connector, to control a rotation speed of the fan.
 2. The control circuit of claim 1, wherein the fan controller comprises a first interface and a second interface, the first interface is connected to the temperature measuring module, the second interface is connected to the conversion circuit.
 3. The control circuit of claim 2, wherein the temperature measuring module comprises a temperature sensor chip, a serial clock pin of the temperature sensor chip is connected to a first pin of the first interface of the fan controller through a first resistor, a serial data pin of the temperature sensor chip is connected to a second pin of the first interface of the fan controller through a second resistor, the serial clock pin and the serial data pin are connected to a first power source respectively through third and fourth resistors, an alarm pin of the temperature sensor chip is connected to the first power source through a fifth resistor, a ground pin of the temperature sensor chip is grounded, a voltage pin of the temperature sensor chip is connected to the first power source and also grounded through a first capacitor, a first data pin of the temperature sensor chip is grounded through a sixth resistor, second and third data pins of the temperature sensor chip are connected to the first power source respectively through seventh and eighth resistors.
 4. The control circuit of claim 3, wherein the conversion circuit comprises first and second transistors, a first pin of the second interface of the fan controller is connected to the first power source through a ninth resistor and also connected to a base of the first transistor through a tenth resistor, an emitter of the first transistor is grounded, a collector of the first transistor is connected to the first power source through an eleventh resistor and also connected to a base of the second transistor, an emitter of the second transistor is grounded, a collector of the second transistor is connected to the first power source through a twelfth resistor and also connected to a control pin of the fan connector.
 5. The control circuit of claim 4, wherein a second pin of the second interface of the fan controller is grounded through thirteenth and fourteenth resistors in sequence, a second capacitor is connected to the fourteenth resistor in parallel, a node between the thirteenth and fourteenth resistors is connected to a second power source through fifteenth and sixteenth resistors in sequence, a node between the fifteenth and sixteenth resistors is connected to an anode of a diode, a cathode of the diode is connected to the second power source and also connected to a measuring pin of the fan connector. 